Generally speaking, the present invention relates to programmable timing devices for appliances and the like and more specifically to such a device which is light activated and includes a plurality of at least partially opaque elements, a means for rotating at least three of the elements in substantially dissimilar cycles, at least two light sources wherein each of the light sources is masked by at least a portion of at least one of the elements and a means responsive to each of the light sources for activating a machine function of the appliance in a programmed sequence of at least two time intervals at at least one power level.
Programmable timing devices are generally of two types; either electronic or mechanical. Such timing devices of the mechanical variety usually include a timer motor which is utilized to drive various cams and/or to operate various electrical contacts. With the utilization of cams, the timer motor is required to drive a substantial load therefore requiring a motor which is capable of handling such loads. Depending upon the load to be driven, the cost of such motors increases or the reliability decreases as the load increases. Furthermore, the life of mechanical timing devices wherein electrical contacts are used is seriously limited, especially when such devices are placed in appliances where a large number of operations are required over the life of the timer. Because of the various mechanisms found in most mechanical timers, it is a well-known fact that many such timers either are not precise or lose their precision over their life. While many of the problems associated with mechanical timing devices have been overcome by electronic timers utilizing all solid state components, such systems many times become complex and are considerably more expensive than the conventional mechanical timer.
Timing devices which may be programmed to time a sequence of functions of an appliance at various time intervals are generally known in the art. However, many appliances now require that a single function of the appliance be timed during at least two time intervals at more than one power level. Although this invention is not intended to be limited hereto, the microwave oven is a typical example of such appliance. When cooking frozen food, it is many times desirable to defrost the food at a low power level for one programmed interval of time and to subsequently cook the food at a substantially higher power level for another programmed interval of time. During each programmed time interval, the magnetron power supply of the microwave oven must be actuated at either a low or high power level depending upon the programmed interval being timed. Utilization of conventional mechanical or electronic programmable timing devices to perform these types of functions in an appliance would result in the problems previously enumerated. Accordingly, there exists a need for a simple, inexpensive, reliable, and precise timing mechanism which would abate the aforementioned problems and be capable of being programmed for at least two time intervals at more than one power level.